1. Field of the Invention
The surface propeller or surface piercing propeller is a partially submerged naturally ventilated propeller that during normal forward movement of the marine vessel achieves all of its thrust from blade face pressure because the blade back is nearly or completely ventilated. Based on this functionality the blade front (or blade face) may be referred to as the pressure face and the blade back as the vacuum face.
2. Description of the Related Art
The function of a surface propeller is based upon basic principles which have been generally accepted for many decades. Application of the basic principles to actual operating conditions, however, involves the interplay of many complex variables caused by the three dimensional complex blade face surfaces of the propeller. Consequently, the effective functioning of a propeller blade, although theoretically simple, is actually extremely complex, especially at high operational speeds, as is well known to those in this art. Therefore surface propeller designers constantly experiment with propeller variations and periodically discover blade geometries that empirically function unexpectedly well, or unexpectedly poorly, for reasons that are not fully understood.
Achieving improvements in blade geometries occurs after long periods of trial and error experimentation with different configuration variations. Those skilled in the art have in the past, by the above described process, experimented, developed and successfully applied various features to the marine surface propeller trailing edge to increase thrusting efficiency using geometric structures such as the cup, ramp or interceptor.
Effective performance of the surface piercing propeller during forward movement depends upon obtaining pressure on the front face of the propeller, which results in the propeller's thrust. The back side of the propeller, the vacuum side, is in a void or cavity which is naturally ventilated from the surface air, and so provides substantially no pressure either positive or negative. Thus, effective performance also depends on minimizing pressure on a blade back.
In order to maximize blade face pressure almost all known surface propellers existing today have a geometry consisting of a flat or cambered pressure face with an annex at the trailing edge which can be a ramp, cup, interceptor or any geometric addition at the trailing edge to create a pressure peak at this point. This results in surface propellers having a pressure peak at the leading edge and a second pressure peak at the trailing edge. However, the central portion of the blade face chord is a low pressure zone between these two pressure peaks, which fails to maximize the pressure on the blade face.
Thus, current surface piercing propeller blades fail to maximize their thrust for a given rotational velocity (RPM) and size (effective radius or surface area). In addition, there are no known features for the back side of a surface propeller directed toward minimizing pressure.
Because prior art surface propeller blades fail to provide a solution to the problem of providing a highly efficient and compact propeller blade then what is needed is a surface piercing propeller blade that maximizes the thrusting force by maximizing pressure for a given area on the blade pressure face and minimizing the pressure for a given area on the blade vacuum face.